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Joule vs. Erg — What's the Difference?

By Tayyaba Rehman & Maham Liaqat — Updated on April 26, 2024
A joule is the SI unit of energy, representing the amount of work done when a force of one newton is applied over a meter, while an erg is a much smaller unit, used in the CGS system, equal to 10^-7 joules.
Joule vs. Erg — What's the Difference?

Difference Between Joule and Erg

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Key Differences

A joule, defined as one newton meter, is the standard unit of energy in the International System of Units (SI), which is widely used in science and engineering globally. Whereas, an erg is the unit of energy in the centimeter-gram-second (CGS) system of units, and it is primarily used in physics, especially in electromagnetic contexts.
Joules are typically used to express larger quantities of energy, such as in electrical energy consumption or mechanical work, making it suitable for everyday practical applications. On the other hand, ergs, being significantly smaller, are more convenient for theoretical physics calculations, particularly when dealing with microscopic systems like atoms and molecules.
The conversion between joules and ergs is straightforward, with one joule equaling 10^7 ergs. This reflects the erg's utility in fields where precise, small energy measurements are required, whereas joules are practical for larger-scale applications.
In practical usage, joules are seen on energy bills, in discussions of food energy (calories), and when talking about the energy consumption of appliances. Conversely, ergs might be encountered in scientific literature and studies involving particle physics, where extremely small energy measurements are necessary.
Educational contexts also differ in their use of these units; joules are part of the curriculum in general science education across the world due to their relevance to everyday life, while ergs are typically taught in more specialized physics courses focusing on the CGS system.
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Comparison Chart

System of Units

International System of Units (SI)
Centimeter-gram-second (CGS) system

Typical Usage

General and practical applications
Specialized scientific contexts

Size

Larger unit
Smaller unit (1 joule = 10^7 ergs)

Common Applications

Electrical energy, mechanical work
Theoretical physics, particle physics

Educational Context

Taught in general science education
Taught in specialized physics courses

Compare with Definitions

Joule

A joule is a unit of energy equal to the work done by a force of one newton moving an object one meter.
Lifting a small apple one meter up in the air expends about one joule of energy.

Erg

Due to its small size, an erg is practical in theoretical physics for energy calculations.
Electromagnetic energy in a light wave might be calculated in ergs.

Joule

In terms of heat energy, one joule is the amount required to raise the temperature of a gram of water by 0.24 degrees Celsius.
Heating a swimming pool during winter requires billions of joules.

Erg

Ergs measure work in a similar way to joules but on a much smaller scale.
Pushing a pencil across a desk might use thousands of ergs.

Joule

Joules can also express kinetic energy,
A moving car has kinetic energy measured in millions of joules.

Erg

An erg is a small unit of energy in the CGS system, suitable for microscopic energy scales.
A single molecule's kinetic energy might be a few ergs.

Joule

Joules are used to measure electrical energy, such as kilowatt-hours converted to joules.
A 60-watt bulb running for an hour uses 216 kilojoules.

Erg

Ergs can also describe energy in terms of heat, especially in controlled physics experiments.
The heat energy added in a microscopic chemical reaction is often measured in ergs.

Joule

Joules are applicable in nutrition to describe food energy, often compared to calories.
A dietary calorie is approximately 4184 joules.

Erg

Ergs are often used in astrophysics and particle physics calculations.
The energy released in particle collisions can be measured in ergs.

Joule

The joule ( jowl, jool; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre (1 newton-metre or N⋅m).

Erg

The erg is a unit of energy equal to 10−7 joules (100 nJ). It originated in the centimetre–gram–second (CGS) system of units.

Joule

The International System unit of electrical, mechanical, and thermal energy, equal to the work done when a force of one newton acts through a distance of one meter, and also equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second.

Erg

The centimeter-gram-second unit of energy or work equal to the work done by a force of one dyne acting over a distance of one centimeter.

Joule

In the International System of Units, the derived unit of energy, work and heat; the work required to exert a force of one newton for a distance of one metre. Equivalent to one watt of power for a duration of one second. Symbol: J

Erg

An extensive area of desert covered with shifting sand dunes.

Joule

A unit of work which is equal to 107 ergs (the unit of work in the C. G. S. system of units), and is equivalent to one watt-second, the energy expended in one second by an electric current of one ampere in a resistance of one ohm; also called the absolute joule. It is abbreviated J or j. The international joule is slightly larger, being 1.000167 times the absolute joule. The absolute joule is approximately equal to 0.737562 foot pounds, 0.239006 gram-calories (small calories), and 3.72506 x 10-7 horsepower-hours, and 0.000948451 B.t.u.

Erg

The unit of work or energy, being the amount of work done by a force of one dyne applied through a distance of one centimeter. Equal to 10−7 joules.

Joule

A unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second

Erg

(geomorphology) A large desert region of sand dunes with little or no vegetation, especially in the Sahara.

Joule

English physicist who established the mechanical theory of heat and discovered the first law of thermodynamics (1818-1889)

Erg

An ergometer.

Erg

To use an ergometer.
I erg every morning.
She erged a steady state piece.

Erg

The unit of work or energy in the C. G. S. system, being the amount of work done by a dyne working through a distance of one centimeter; the amount of energy expended in moving a body one centimeter against a force of one dyne (981 dynes exert the same force as a one gram mass in the earth's gravitational field). One foot pound is equal to 13,560,000 ergs. The absolute Joule is equivalent to 107 ergs, which are equivalent to 0.2389 gram-calories at 15° C. See also mechanical equivalent of heat under equivalent.

Erg

A cgs unit of work or energy; the work done by a force of one dyne acting over a distance of one centimeter

Common Curiosities

Can you convert joules to ergs easily?

Yes, converting joules to ergs is straightforward: 1 joule equals 10^7 ergs.

How are joules and ergs related in terms of energy units?

Both joules and ergs measure energy, but joules are part of the SI system and ergs are part of the CGS system, reflecting different scales and usage contexts.

Are joules relevant in everyday life?

Yes, joules are very relevant in everyday life, especially in measuring electrical energy usage and the caloric content of foods.

In what educational settings might I learn about ergs?

Ergs are typically taught in specialized physics courses, particularly those focusing on the CGS system and theoretical aspects of physics.

Is there a practical example where using ergs is more beneficial than joules?

Ergs are more beneficial in theoretical and microscopic physics, where dealing with extremely small energy quantities is common.

Why might a scientist choose to use ergs instead of joules?

A scientist might choose ergs for precision in small-scale energy calculations, typical in fields like quantum mechanics and particle physics.

What kind of practical applications involve ergs?

Practical applications of ergs are mostly limited to scientific research, such as in studies of electromagnetic fields and radiation.

How are joules used in relation to food?

Joules are used to express the energy content in food, where 1 dietary calorie is approximately 4184 joules.

What is the physical significance of an erg in scientific research?

In scientific research, ergs are crucial for measuring very small energy levels, such as in particle physics and astrophysics.

What industries rely heavily on the use of joules?

Industries such as electrical power, mechanical engineering, and health (in terms of dietary energy) heavily rely on the use of joules.

What historical developments led to the adoption of joules and ergs?

The adoption of joules followed developments in mechanical and electrical engineering, while ergs were adopted due to their utility in early 20th-century physics.

How does the usage of joules impact daily technology?

Joules directly impact daily technology in aspects like power consumption in household appliances and energy efficiency ratings.

How do joules and ergs help in environmental science?

Joules help in calculating the energy efficiency and carbon footprint of various processes, while ergs might be used in modeling microscopic environmental interactions.

What are the educational prerequisites to understand joules and ergs?

A basic understanding of physics and mathematics is needed to grasp the concepts of joules and ergs, with advanced studies required for deeper understanding, especially for ergs.

Are there specific scientific instruments designed to measure ergs or joules?

Yes, calorimeters measure energy in joules for heat changes, while specialized sensors in physics experiments might measure energy in ergs.

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Author Spotlight

Written by
Tayyaba Rehman
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Maham Liaqat

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